Microscopic investigation of single-crystal diamond following ultrafast laser irradiation

We present a structural investigation of single-crystal diamond following ultrafast laser irradiation of the surface and the bulk material. Optical microscopy, atomic force microscopy, scanning electron microscopy, and focused-ion beam and transmission electron microscopy techniques were utilized to selectively examine the final state of the samples. Laser induced periodic surface structures (LIPSS) with high- and low-spatial frequencies were obtained with multiple-pulse surface irradiation under both stationary and translated target conditions. High magnification transmission electron microscopy analysis of cross sections of the LIPSS revealed modified layers of a few tens of nanometers in thickness capping the crystalline diamond matrix. Sub-surface irradiation of diamond at high laser fluences led to damaged regions and cracks in the bulk material. When translational bulk irradiation of the diamond was performed, substantially sub-wavelength periodic structures were observed at the unpolished side facet of the diamond plate where the laser focus was translated out of the bulk. Spatial periods were 140 nm and the structures largely consisted of single-crystal diamond with a 10 nm modified layer. Finally, preliminary studies of single-shot laser ablation craters at high laser fluences exhibited suppression of material removal for peak values above 45 J/cm².